S&F Ref: 743299 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address NEC Infrontia Corporation, of 2-6-1, Kitamikata, Takatsu of Applicant: ku, Kawasaki-shi, Kanagawa, Japan Actual Inventor(s): Shinsuke Miura Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Housing structure of an apparatus and a subsidiary cover opening/closing structure The following statement is a full description of this invention, including the best method of performing it known to me/us:- 1 HOUSING STRUCTURE OF AN APPARATUS AND A SUBSIDIARY COVER OPENING/CLOSING STRUCTURE Field of the Invention This invention relates to a housing structure of an apparatus, such as an 5 electronic apparatus, and, in particular, to a structure for opening and closing a subsidiary cover covering an area having an internal worksite, such as a wiring portion of a main apparatus. Background of the Invention In the past, proposal has been made of various housing structures for an 1o apparatus. For example, Japanese Unexamined Patent Application Publication (JP-A) No. H8-78861 (Patent Document 1) discloses a housing structure of an electronic apparatus, which makes it easy to attach and detach a cover of the electronic apparatus so that installation and maintenance of the electronic apparatus are safely and quickly carried out. In the housing structure disclosed in the above-mentioned publication, the cover of a is housing of the electronic apparatus is divided into a main cover and a subsidiary cover. The subsidiary cover is attached to a base by an engaging structure comprising protrusions formed on the subsidiary cover and slits formed on the base. More in detail, the cover comprises the main cover which is never removed in principle and the subsidiary cover which may be removed if necessary. The subsidiary cover is attached to 20 the base by engagement between the protrusions formed on opposite side surfaces of the subsidiary cover and the slits formed on opposite side surfaces of the base and by fastening a screw through a hole formed on a front surface of the subsidiary cover and a hole formed on a front surface of the base. Japanese Unexamined Patent Application Publication (JP-A) No. H4-177796 25 (Patent Document 2) discloses a housing structure of an electronic apparatus, such that a cover can be fixed to a case without using a fastening screw. In the housing structure disclosed in the publication, a housing accommodating an electronic parts unit comprises a case having an opening on one surface, a main cover covering the opening of the case, and a subsidiary cover covering a battery container. By sliding the main cover with 30 respect to the case, a rib formed on the main cover is engaged with a groove formed on the case to lock one end of the main cover. By press-fitting a locking portion formed at the other end of the main cover into a cutout formed on the case, the main cover is inhibited from sliding. By sliding the subsidiary cover with respect to the case, a rib 2 formed on the subsidiary cover is engaged with a groove formed on the case to lock the subsidiary cover with respect to the case. Simultaneously, the main cover and the subsidiary cover are engaged with each other to inhibit sliding of the subsidiary cover. Japanese Unexamined Patent Application Publication (JP-A) No. 2003-326805 5 (Patent Document 3) discloses a cover attaching method which is for use in a line printer housing comprising a base portion and an exterior cover and which is capable of improving a sound insulation effect at an engaging portion between the base portion and the exterior cover and of easily attaching and detaching even a relatively large-sized cover of an integral structure. The base portion is provided with guide rails formed on left and 1o right sides of an upper part thereof The exterior cover has two longitudinal engaging portions slidable along the guide rails. The exterior cover is attached to the base portion by sliding along the guide rails formed on the left and the right sides of the base portion. Since the engaging portion between the guide rails and the exterior cover is kept airtight, the sound insulation effect is improved. Further, the exterior cover is fixed by a screw at i5 the engaging portion. Therefore, positioning of the exterior cover is unnecessary when it is attached. Thus, the exterior cover is easily handled in combination with the guide rails. Japanese Unexamined Patent Application Publication (JP-A) No. H 11-1 72991 (Patent Document 4) discloses a locking mechanism capable of fixing a locked member to a main body of a locking member by a pressing operation. The locking mechanism 20 disclosed in the publication comprises an engaging arrangement formed on the main body of the locking member and a locking arrangement. When an engaged portion of the locked member is set at a predetermined position, the engaging arrangement is engageable with the engaged portion, and is engaged with the engaged portion by the pressing operation. The locking arrangement locks the engaging arrangement when the 25 engaging arrangement is engaged with the engaged portion. The electronic apparatus may be a main apparatus of a key telephone set or the like. The main apparatus may be placed on a floor or at a high position in a room. In case where the main apparatus is placed on a floor, a subsidiary cover is preferably removed in order to facilitate a work of an operator. On the other hand, if the main 30 apparatus is placed at a high position, the subsidiary cover is preferably fixed in an opened state in order to facilitate a work of an operator. Traditionally, however, as disclosed in the above-mentioned Patent Document 1, the subsidiary cover covering a worksite of the main apparatus is fixed to an apparatus main body by the use of the screw when the subsidiary cover is in a closed state.
3 Therefore, in order to open the subsidiary cover at the time of a work, a tool is required. Further, the screw removed by the tool must be kept until termination of the work. In addition, the subsidiary cover removed during the work must be kept also until termination of the work. Therefore, if the work is performed at a high position, the s operator must bring the subsidiary cover to another place (low position) so that the work is not obstructed. Thus, an extra operation is required and a workability is impaired. In case where the subsidiary cover can be fixed to the apparatus-main body in an opened state, the subsidiary cover is generally fixed by the use of a separate part such as a support rod. This results in a disadvantage in view of workability, productivity, and cost. 10 In the Patent Document 2, the main cover and the sub cover can be attached to the case without using a fastening screw. However, in the structure disclosed in the Patent Document 2, the subsidiary cover can be merely attached to and detached from the case. The subsidiary cover can not be fixed to the case in an opened state. The Patent Document 3 merely discloses the line printer housing in which the 15 exterior cover is slidable with respect to the base portion. The exterior cover is attached to the base portion by the fastening screw. Accordingly, there is a disadvantage similar to that mentioned in connection with the Patent Document 3. The Patent Document 4 merely discloses the locking mechanism capable of fixing the locked member to the main body of the locking member. In other words, the 20 Patent Document 4 merely discloses the locking mechanism for locking a closed state of the locked member when the locked member is closed with respect to the main body of the locking member. The Patent Document 4 does neither disclose nor suggest a locking mechanism for locking an opened state of the locked member when the locked member is opened with respect to the main body of the locking member. 25 Object of the Invention It is an object of the present invention to overcome or ameliorate some of the disadvantages of the prior art, or at least to provide a useful alternative. 30 Summary of the Invention The present invention provides a housing structure of an apparatus, which includes a main cover and a subsidiary cover, said main cover and said subsidiary cover covering an apparatus-main body, wherein: 4 said main cover has a shape covering an upper front side of said apparatus-main body, said subsidiary cover having a shape covering a lower front side of said apparatus main body; said housing structure comprising: s an opening/closing mechanism enabling said subsidiary cover to be opened and closed with respect to said apparatus-main body; a first locking arrangement for locking a closed state of said subsidiary cover when said subsidiary cover is closed with respect to said apparatus-main body; and a second locking arrangement for locking an opened state of said subsidiary 1o cover when said subsidiary cover is opened with respect to said apparatus-main body; and wherein said apparatus-main body has an insert hole, said second locking arrangement comprises a main claw extending upward from an upper end of said subsidiary cover and said insert hole formed on said apparatus-main body to receive said main claw inserted therein. i5 The present invention also provides a subsidiary cover opening/closing structure having a subsidiary cover openable and closable with respect to an apparatus-main body, wherein: said subsidiary cover opening/closing structure is adapted to lock a closed state of said subsidiary cover without using a screw when said subsidiary cover is closed with 20 respect to said apparatus-main body and to lock an opened state of said subsidiary cover without using an additional part when said subsidiary cover is opened with respect to said apparatus-main body; and wherein: said subsidiary cover is locked in said closed state by engaging a main claw with a main rib when said subsidiary cover is put into said closed state; 25 said subsidiary cover being locked in said opened state after said closed state by pushing an upper part of said main claw by a finger from an outer surface of an apparatus to disengage said main claw from said main rib so that said closed state is unlocked, sliding said subsidiary cover downward along rails, rotating said subsidiary cover upward to lift said subsidiary cover, pushing said subsidiary cover into said apparatus-main body, 30 pushing said main claw into an insert hole of said apparatus-main body, and engaging a second claw with a second rib of said apparatus-main body so as to lock said opened state. The present invention further provides a subsidiary cover opening/closing structure having a subsidiary cover openable and closable with respect to an apparatus 35 main body, wherein: 4a said subsidiary cover opening/closing structure is adapted to lock a closed state of said subsidiary cover without using a screw when said subsidiary cover is closed with respect to said apparatus-main body, to lock an opened state of said subsidiary cover without using an additional part when said subsidiary cover is opened with respect to said 5 apparatus-main body, and to remove said subsidiary cover from said apparatus-main body; and wherein said subsidiary cover is locked in said closed state by engaging a main claw with a main rib when said subsidiary cover is put into said closed state; said subsidiary cover being locked in said opened state after said closed state by 1o pushing an upper part of said main claw by a finger from an outer surface of an apparatus to disengage said main claw from said main rib so that said closed state is unlocked, sliding said subsidiary cover downward along rails, rotating said subsidiary cover upward to lift said subsidiary cover, pushing said subsidiary cover into said apparatus-main body, pushing said niain claw into an insert hole of said apparatus-main body, and engaging a is second claw with a second rib of said apparatus-main body so as to lock said opened state; said subsidiary cover being removed from said apparatus-main body by removing said subsidiary cover from cutout portions of said rails when said subsidiary cover slides along said rails. 20 Brief Description of the Drawings A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: 25 Fig. 1 is a perspective view of a housing structure of an apparatus according to an embodiment of this invention when a subsidiary cover is closed; Fig. 2 is a perspective view of the housing structure in Fig. I when the subsidiary cover is opened; Fig. 3 is a perspective view of the housing structure in Fig. I when the subsidiary 30 cover is opened; 5 Fig. 4 is a front perspective view of the subsidiary cover of the housing structure illustrated in Fig. 1; Fig. 5 is a rear perspective view of the subsidiary cover of the housing structure illustrated in Fig. 1; 5 Fig. 6 is an enlarged front perspective view of a main claw formed on the subsidiary cover illustrated in Figs. 4 and 5; Fig. 7 is an enlarged rear perspective view of the main claw formed on the subsidiary cover illustrated in Figs. 4 and 5; Fig. 8 is an enlarged front perspective view of a second subsidiary claw formed io on the subsidiary cover illustrated in Figs. 4 and 5; Fig. 9 is an enlarged rear perspective view of a right rail formed on the subsidiary cover illustrated in Figs. 4 and 5; Fig. 10 is an enlarged rear perspective view of a left rail formed on the subsidiary cover illustrated in Figs. 4 and 5; 15 Fig. 11 is a front perspective view of an apparatus-main body and a main cover used in the housing structure illustrated in Fig. 1; Fig. 12 is an enlarged front perspective view showing an area around a right operation shaft attached to the apparatus-main body illustrated in Fig. 11; Fig. 13 is an enlarged front perspective view showing an area around a left 20 operation shaft attached to the apparatus-main body illustrated in Fig. 11; Fig. 14 is a perspective view for describing an operation of the housing structure illustrated in Fig. 1 when the main claw is pushed from a front side; Fig. 15 is a perspective view for describing the operation of the housing structure illustrated in Fig. 1 when the subsidiary cover is pulled down along the rails; 25 Fig. 16 is a perspective view for describing the operation of the housing structure illustrated in Fig. 1 when the subsidiary cover is removed from the apparatus-main body; Fig. 17 is a perspective view for describing the operation of the housing structure illustrated in Fig. 1 when the subsidiary cover is rotated frontward and upward around the operation shafts of the apparatus-main body to be lifted; 30 Fig. 18 is a perspective view for describing the operation of the housing structure illustrated in Fig. I when the subsidiary cover is pushed into the apparatus-main body with the main claw inserted into an insert hole and the subsidiary claw locked by a subsidiary rib; and 6 Fig. 19 is an enlarged sectional view for describing the operation of the housing structure illustrated in Fig. 1, showing the positional relationship between the right operation shaft and the right rail when the subsidiary cover is removed from the apparatus-main body. 5 Detailed Description of the Preferred Embodiments Now, an embodiment of this invention will be described in detail with reference to the drawings. Referring to Figs. 1 through 3, an apparatus 10 to which this invention is applicable is a main apparatus of a key telephone set or the like. The main apparatus 10 is 1o placed on a floor or at a high position in a room. The main apparatus 10 comprises an apparatus-main body 11 and a cover covering a front side of the apparatus-main body 11. The cover comprises a main cover 13 covering an upper front side of the apparatus-main body 11 and a subsidiary cover 15 covering a lower front side of the apparatus-main body 11. 15 The main cover 13 is never removed in principle. The subsidiary cover 15 is openable and closable with respect to the apparatus-main body 11 and can be removed from the apparatus-main body 11. In Fig. 1, the subsidiary cover 15 is closed with respect to the apparatus-main body 11. In Figs. 2 and 3, the subsidiary cover 15 is opened with respect to the apparatus 20 main body 11. The subsidiary cover 15 covers a worksite 17 at a lower part of the apparatus main body 11. The worksite 17 is, for example, a wiring portion of the main apparatus 10. In case where the main apparatus 10 is placed on a floor, the subsidiary cover 15 is preferably removed from the apparatus-main body 11 so as to facilitate a work of an 25 operator at the worksite 17. On the other hand, in case where the main apparatus 10 is placed at a high position, the subsidiary cover 15 is preferably fixed to the apparatus-main body in an opened state as illustrated in Fig. 3 so as to facilitate the work of the operator at the worksite 17. Referring to Figs. 4 and 5, the subsidiary cover 15 comprises a front plate 21 30 formed on a front side, a right side plate 22 extending rearward from a right side end of the front plate 21, a left side plate 23 extending rearward from a left side end of the front plate 21, and a bottom plate 24 extending rearward from a lower end of the front plate 21.
7 The front plate 21 has a front surface 21a and a back surface 21b. The back surface 21b of the front plate 21 is provided with a main claw 31 formed at the center of its upper end and protruding upward. The bottom plate 24 is provided with a pair of first subsidiary claws 32 formed at two positions at an inner end (rear end) thereof and 5 protruding upward. The first subsidiary claws 32 are used upon closing the subsidiary cover 15. In this embodiment, the number of the first subsidiary claws 32 is two. However, the number of the first subsidiary claws 32 may be one or three or more. The back surface 21b of the front plate 21 is provided with a pair of second subsidiary claws 33 formed on its upper end in the vicinity of opposite side surfaces and io protruding upward. The second subsidiary claws 33 are used upon opening the subsidiary cover 15. Further, the back surface 21b of the front plate 21 is provided with a right rail 35 formed inward of the right-side second subsidiary claw 33 and a left rail 36 formed inward of the left-side second subsidiary claw 33. Referring to Figs. 6 and 7, the main claw 31 is seen from a front side. Referring 15 to Fig. 7, the main claw 31 is seen from a back side. As seen from the figures, the main claw 31 has a protrusion 311 protruding forward. Referring to Fig. 8, the second subsidiary claw 33 is seen from the front side. Referring to Fig. 9, the right rail 35 is seen from the back side. Referring to Fig. 10, the left rail 36 is seen from the back side. 20 As shown in Fig. 9, the right rail 35 has a rail portion 351 spaced rearward from the back surface 21b of the front plate 21 and vertically extending in parallel to the back surface 21b. The rail portion 351 has a pair of cutout portions 351a formed at its intermediate portion and cut out inward from left and right sides. The rail portion 351 has an inverted-J shaped upper end portion and a J-shaped lower end portion. 25 As shown in Fig. 10, the left rail 36 has a rail portion 361 spaced rearward from the back surface 21b of the front plate 21 and vertically extending in parallel to the back surface 21b. The rail portion 361 has a pair of cutout portions 361a formed at its intermediate portion and cut out inward from left and right sides. Like the rail portion 351, the rail portion 361 has an inverted-J shaped upper end portion and a J-shaped lower 30 end portion. The cutout portions 351a and 361a serve to insert and remove operation shafts (which will later be described) with respect to the rail portions 351 and 361. The rail portions 351 and 361 have curved portions at their upper ends. The curved portions serve 8 to support the subsidiary cover 15 so that the subsidiary cover 15 is rotatable around the operation shafts. Referring to Fig. 11, the main cover 13 has a main claw insert hole 41 formed at the center of its lower end to receive the main claw 31 inserted therein when the 5 subsidiary cover 15 is closed. The main cover 13 has a main rib 41a (Fig. 1) formed in the main claw insert hole 41 to be engaged with the protruding portion 311 of the main claw 31. The apparatus-main body 11 is provided with a pair of first subsidiary claw insert holes 42 formed at two positions at a rear lower end thereof to receive the first subsidiary 10 claws 32 inserted therein when the subsidiary cover 15 is closed. The main cover 13 is provided with a pair of second subsidiary claw insert holes 43 formed on its lower end in the vicinity of opposite sides to receive the second subsidiary claws 33 inserted therein when the subsidiary cover 15 is closed. On the other hand, the apparatus-main body 11 is provided with a main claw is insert hole 45 formed below the main claw insert hole 41 to receive the main claw 31 inserted therein when the subsidiary cover 15 is opened. The apparatus-main body 11 is provided with a right subsidiary rib 46 formed below the right-side second subsidiary claw insert hole 43 to lock the right-side second subsidiary claw 33 when the subsidiary cover 15 is opened. The apparatus-main body 11 is provided, below the left-side second 20 subsidiary claw insert hole 43, with a left-side subsidiary rib 47 for locking the left-side second subsidiary claw 33 when the subsidiary cover 15 is opened and with a second subsidiary claw insert hole 48 for receiving the left-side second subsidiary claw 33 inserted therein when the subsidiary cover 15 is opened. Thus, the second subsidiary claw insert hole 48 is formed at a lower end of the left-side subsidiary rib 47. 25 The apparatus-main body 11 is provided with the right operation shaft 51 formed inward of the right-side subsidiary rib 46 in the vicinity thereof to be inserted into the right rail 35. Similarly, the apparatus-main body 11 is provided with the left operation shaft 52 formed inward of the left-side subsidiary rib 47 in the vicinity thereof to be inserted into the left rail 36. 30 The main cover 13 is provided with a right rail insert hole 56 formed inward of the right-side second subsidiary claw insert hole 43 in the vicinity thereof to receive the right rail 35 inserted therein. Similarly, the main cover 13 is provided with a left rail insert hole 57 formed inward of the left-side second subsidiary claw insert hole 43 in the vicinity thereof to receive the left rail 36 inserted therein.
9 Referring to Fig. 12, the right operation shaft 51 comprises a pair of left and right shafts 511 with a gap 51a left therebetween. Referring to Fig. 13, the left operation shaft 52 comprises a pair of left and right shafts 521 with a gap 52a left therebetween. In the above-mentioned structure, a combination of the right rail 35, the left rail 5 36, the right operation shaft 51, and the left operation shaft 52 acts as an opening/closing mechanism enabling the subsidiary cover 15 to be opened and closed with respect to the apparatus-main body 11. In this embodiment, the opening/closing mechanism comprises a sliding/rotating mechanism by which the subsidiary cover 15 is vertically slidable and rotatable around the upper end of the subsidiary cover 15. 10 A combination of the main claw 31 and the main rib 41a formed in the main claw insert hole 41 serves as a first locking arrangement for locking a closed state of the subsidiary cover 15 when the subsidiary cover 15 is closed with respect to the apparatus main body 11. On the other hand, a combination of the main claw 31 and the main claw insert hole 45 formed on the apparatus-main body 11 serves as a second locking 15 arrangement for locking an opened state of the subsidiary cover 15 when the subsidiary cover 15 is opened with respect to the apparatus-main body 11. As the first locking arrangement locks the closed state of the subsidiary cover 15 when the subsidiary cover 15 is closed with respect to the apparatus-main body 11, the subsidiary cover 15 can be fixed to the apparatus-main body 11 in the closed state without 20 using a screw. As the second locking arrangement locks the opened state of the subsidiary cover 15 when the subsidiary cover 15 is opened with respect to the apparatus main body 11, the subsidiary cover 11 can be fixed to the apparatus-main body 11 also in the opened state without using a separate part such as a screw or a support rod. A combination of the first subsidiary claws 32 and the first subsidiary claw insert 25 holes 42 serves as a closed state-maintaining arrangement for maintaining the closed state of the subsidiary cover 15 in cooperation with the first locking arrangement. A combination of the second subsidiary claws 33, the subsidiary ribs 46 and 47, and the insert hole 48 serves as an opened state-maintaining arrangement for maintaining the opened state of the subsidiary cover 15 in cooperation with the second locking 30 arrangement. Since the closed state-maintaining arrangement maintains the closed state of the subsidiary cover 15 in cooperation with the first locking arrangement, it is possible, in the closed state of the subsidiary cover 15, to reliably fix the subsidiary cover 15 with respect to the apparatus-main body 11 without using a screw. Since the opened state-maintaining 10 arrangement maintains the opened state of the subsidiary cover 15 in cooperation with the second locking arrangement, it is possible, in the opened state of the subsidiary cover 15, to reliably fix the subsidiary cover 15 with respect to the apparatus-main body 11 without using an additional part such as a screw or a support rod. In the illustrated example, the 5 opened state-maintaining arrangement uses the subsidiary ribs 46 and 47 and the insert hole 48 as a locking arrangement for locking the second subsidiary claws 33. However, the locking arrangement is not restricted thereto but may have any other appropriate structure depending upon the structure of the apparatus-main body 11. For example, the locking arrangement may be implemented by the subsidiary ribs alone or the insert hole io alone. Further, a combination of the cutout portion 351a of the right rail 35, the cutout portion 361a of the left rail 36, the gap 51a of the right operation shaft 51, and the gap 52a of the left operation shaft 52 serves as an attaching/detaching arrangement for enabling the subsidiary cover 15 to be attached to and detached from the apparatus-main body 15. Is Since the attaching/detaching arrangement enables the subsidiary cover 15 to be attached to and detached from the apparatus-main body 15, the subsidiary cover 15 is removable from the apparatus-main body 11. Referring to Fig. 1, description will be made of the closed state of the subsidiary cover 15. In this state, the subsidiary cover 15 is fixed to the apparatus-main body 11 by 20 the main claw 31 and the first subsidiary claws 32. In detail, the main claw 31 is inserted into the main claw insert hole 41 formed on the main cover 13 and is engaged with the main rib 41a to lock the closed state of the subsidiary cover 15. On the other hand, the first subsidiary claws 32 are inserted into the first subsidiary claw insert holes 42 to maintain the closed state of the subsidiary cover 15. The second subsidiary claws 33 are 25 inserted into the second subsidiary claw insert holes 43 formed on the main cover 13. The right and the left operation shafts 51 and 52 are inserted into the right and the left rails 35 and 36, respectively. Thus, in this embodiment, by the use of the main claw 31, the main rib 41 a, the first subsidiary claws 32, and the first subsidiary claw insert holes 41, the subsidiary 30 cover 15 can be reliably fixed to the apparatus-main body 11 without using a screw when the subsidiary cover 15 is in the closed state. Referring to Fig. 3, description will be made of the opened state of the subsidiary cover 15. In this state, the subsidiary cover 15 is fixed to the apparatus-main body 11 by the main claw 31 and the second subsidiary claws 33. In detail, the main claw 31 is 11 inserted into the main claw insert hole 45 formed on the apparatus-main body 11 to lock the opened state of the subsidiary cover 15. On the other hand, the right-side second subsidiary claw 33 is locked by the right-side subsidiary rib 46. The left-side second subsidiary claw 33 is locked by the left-side subsidiary rib 47 and is inserted into the 5 second subsidiary claw insert hole 48 to maintain the opened state of the subsidiary cover 15. In this state also, the right and the left operation shafts 51 and 52 are inserted into the right and the left rails 35 and 36, respectively. Thus, in this embodiment, by the use of the main claw 31, the main claw insert hole 45, the second subsidiary claws 33, the right-side subsidiary rib 46, the left-side io subsidiary rib 47, and the second subsidiary claw insert hole 48, the subsidiary cover 15 can be reliably fixed to the apparatus-main body 11 without using an additional part such as a screw or a support rod when the subsidiary cover 15 is in the opened state. Next referring to Figs. 14 to 19, description will be made of an operation of the housing structure. is At first referring to Figs. 14 to 16 and 19, description will be made of an operation of removing the subsidiary cover 15 from the apparatus-main body 11 when the subsidiary cover 15 is fixed to the apparatus-main body 11 in the closed state. Referring to Fig. 14, the subsidiary cover 15 is in the closed state like in Fig. 1. In this state, an upper part of the main claw 13 is pushed inward by a finger from an outer 20 surface of the main cover 13 to disengage the main claw 31 from the main rib 41 a so that the closed state of the subsidiary cover 15 locked by the main claw 13 is unlocked. Next referring to Fig. 15, the subsidiary cover 15 is made to slide downward along the right and the left rails 35 and 36 as depicted by an arrow A. Then, as illustrated in Fig. 19, the subsidiary cover 15 is made to slide slightly 25 upward so that the right and the left operation shafts 51 and 52 are positioned at the cutout portions 35a and 36a of the right and the left rails 35 and 36, respectively. Finally, as illustrated in Fig. 16, the right and the left operation shafts 51 and 52 are pulled out through the cutout portions 35a and 36a of the right and the left rails 35 and 36, respectively. As a consequence, the subsidiary cover 15 is removed from the 30 apparatus-main body 11. Thus, in this embodiment, the right rail 35, the left rail 36, the right operation shaft 51, and the left operation shaft 52 are provided with the cutout portion 35a, the cutout portion 36a, the gap 51a, and the gap 52a, respectively. With this structure, the subsidiary cover 15 can be removed from the apparatus-main body 11. Thus, in case 12 where the main apparatus 10 is placed on a floor, an operator can performs a work at the worksiie 17 while the subsidiary cover 15 is removed from the apparatus-main body 11. In order to fix the subsidiary cover 15 to the apparatus-main body 11 in the closed state after the subsidiary cover 15 is removed from the apparatus-main body 11, an 5 operation reverse to the above-mentioned operation is carried out. Next referring to Figs. 14, 15, 17, and 18, description will be made of an operation of fixing the subsidiary cover 15 to the apparatus-main body 11 in the opened state after the subsidiary cover 15 is fixed to the apparatus-main body 11 in the closed state. 10 At first referring to Fig. 14, the subsidiary cover 15 is in the closed state. The upper part of the main claw 13 is pushed inward by a finger to unlock the closed state of the subsidiary cover 15. Next referring to Fig. 15, the subsidiary cover 15 is made to slide downward along the right and the left rails 35 and 36 as depicted by the arrow A. Next referring to Fig. 17, the subsidiary cover 15 is rotated frontward and 15 upward by 900 around the right and the left operation shafts 51 and 52 as depicted by an arrow B to lift the subsidiary cover 15. Next referring to Fig. 18, the subsidiary cover 15 is pushed into the apparatus main body 11 as depicted by an arrow C and the main claw 31 is inserted into the main claw insert hole 45. Simultaneously, the second subsidiary claws 33 are locked by the 20 subsidiary ribs 46 and 47. At this time, the left-side second subsidiary claw 33 is inserted into the second subsidiary claw insert hole 48. As a consequence, the subsidiary cover 15 is fixed to the apparatus-main body 11 in the opened state. As described above, in this embodiment, the subsidiary cover 15 can be reliably fixed to the apparatus-main body 15 without using an additional part such as a screw or a 25 support rod when the subsidiary cover 15 is in the opened state. Thus, in case where the main apparatus 10 is placed at a high position in a room, the operator can perform a work at the worksite 17 while the subsidiary cover 15 is fixed to the apparatus-main body 11 in the opened state. Accordingly, it is possible to improve the workability and the productivity as well as to reduce the cost. 30 In order to fix the subsidiary cover 15 to the apparatus-main body 11 in the closed state after the subsidiary cover 15 is fixed to the apparatus-main body 11 in the opened state, an operation reverse to the above-mentioned operation is carried out. While this invention has thus far been disclosed in conjunction with the preferred embodiment thereof, it will be readily possible for those skilled in the art to put this 13' invention into practice in various other manners within the scope of this invention. For example, depending upon the shape of the apparatus, the main claw may be formed at a lateral side (side edge) of the subsidiary cover while a side wall of the 'apparatus-main body may be provided with a hole (for example, a cross hole) for insertion of the main 5 claw. In this case, the subsidiary cover is put into the opened state and the closed state by horizontal sliding movement. In the foregoing embodiment, description has been made about the case where- the apparatus is the main apparatus of the key telephone set. However, this invention is applicable to various electronic apparatuses, for example, a main apparatus of telecommunication equipment and home electric appliance such as an 10 air conditioner, each of which has a subsidiary cover opened by an operator upon a work or maintenance. It is noted here that the apparatus is not limited to the electronic apparatus. Further, this invention is also applicable to a cover of a battery case of home electric appliance or the like. This invention essentially comprises the opening/closing mechanism, the first locking arrangement, and the second locking arrangement. Other 15 components such as the attaching/detaching arrangement, the closed state-maintaining arrangement, and the opened state-maintaining arrangement may selectively be provided if necessary.